2001 3.0i, closing in on 200k miles.
Car runs great other than ...
The "oxygen sensor heater" readiness monitor is not completing (according to my Foxwell), so the car can not be smogged.
I have NO CODES, either OBD or BMW. All other readiness monitors show as ready (7) or not applicable (2). All but this one incomplete monitor reset within a day or two of the last code reset, but this last one refuses to complete, even after a couple of hundred miles over several days.
I've read up a lot on this on the tubes and the most believable answer seems to be that I do actually have an issue with one of my O2 sensors. Not enough of a problem to set a code, but enough to not let the test complete. Weird.
https://www.nyvip.org/PublicSite/OBD...r-monitor.html
https://www.bimmerfest.com/threads/s....576621/page-2
https://www.bimmerfest.com/threads/b....926859/page-2
I replaced the upstream O2 sensors with new Bosch 13477 at 170k miles when I first got the car and hoped for an improvement in mpg that did not follow. The downstream sensors (Bosch 15109) are original.
Questions:
Agree with the plan to replace the downstream O2 sensors?
Can that readiness issue be caused by upstream, downstream, or either type?
Any testing or live data analysis I can do to learn anything before making the repair?
I've seen a ton of discussion about the federal test procedure drive cycle, but no explanation for why my driving very quickly reset all monitors but this one, so am doubting at this point that further driving will guarantee completion. ???
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Background on how I got here:
Service Engine Soon light came on, right before my bi-annual CA smog check. OBD2 P0444 code / BMW "44: DME: Activation, solenoid valve; tank ventilation" code, both pointing to a gas cap or evap purge valve.
The original purge valve ( 13-90-1-433-603 - Fuel Tank Breather Valve) tested electrically and mechanically (~28 Ohms, solenoid clicking strongly when actively tested with Foxwell, air flow confirmed to be open/blocked when doing that testing) perfectly. But I eventually ran out of other possibilities and found enough reports saying that the purge valve might bench test perfectly and still throw the code, and also that non-Genuine-BMW replacements could be similarly bad.
So I replaced with a BMW valve, reset the code, and it has been perfect other than this monitor readiness issue. No code has come back.
And now if I find similar result with the O2 sensors (test fine, but won't let readiness complete), I will not be surprised.